Field of the Invention
This invention relates to a mechanical-magnetic connecting structure, i.e. a mechanical lock, which closes supported by magnetic force and in particular is utilized as closure on bags, rucksacks and comparable objects, wherein this enumeration should not limit the field of use of the invention. Such connecting structure is described in the document WO 2008/006357. This magnetic closure consists of a two-part magnetic system, so that the two closure halves attract and mechanically lock each other from a predetermined minimum distance. With this mechanical lock the magnetic force urges a locking piece against a resilient and hence yielding locking element. The locking piece and the resilient locking element overlap or undercut each other in the condition snapped into place. For opening the closure, the locking piece is shifted with respect to the locking element until a non-engagement position is reached, in which the two elements no longer are in engagement, i.e. the mechanical lock is released. With this shifting, the magnetic system simultaneously is moved into a position in which the magnetic force of attraction either is weakened considerably or a repulsive force is applied, which opens the closure. The magnetic system only insignificantly contributes to the stability and strength of the closure, but only serves to allow a haptically good closing and opening of the closure.
The loadability of the closure is determined by the mechanical lock and substantially depends on how large the overlap surface or the undercut surface of the lock is. The larger the overlap surface or the undercut surface, the greater the mechanical stability of the lock, when all components of the closure are constructed adequately. The possibilities for forming the overlap surface or the undercut surface as large as possible are limited for several reasons, which will be explained below:
It is a specific property of a pawl closure snapping into place according to the prior art described in WO 2008/006357 that the same only has the required stability and loadability when the resilient element is dimensioned sufficiently strong, which inevitably also involves a greater spring force. To ensure that the snap-in process can be effected on its own, i.e. exclusively by means of magnetic force, a magnet adapted to the spring force is required. In other words, the resilient element must have a sufficient mechanical stability, in order to ensure the desired locking function. However, this requires a sufficiently strong magnet. Thus, two mutually exclusive requirements are placed on the magnet: The magnet must be strong enough to overcome the spring force, and the magnet should be as small and light as possible, in order to reduce the costs and the weight.
In the closures known from the prior art WO 2008/006357 there is also a second problem, which in a rotary closure results from the following facts: The most common magnetic system has two magnetic poles per magnetic element and for opening is rotated from an attracting position by about 120° into an at least partly repelling position. In this position, the magnetic force of repulsion supports the opening of the closure. However, to enable the closure to open on its own, the mechanical lock must be out of engagement.
In other words: There is only one predetermined angular range available for locking. This angular range cannot be increased, as from the maximum available 360 degrees a predetermined angular range is required, in which the locking elements must be out of engagement. The available angular range of the closed condition, however, even is substantially smaller, since opening should only be effected when the magnets have reached a position in which they at least partly repel each other, in order to obtain the desired pleasant opening haptics of the closure. Since the overlap or undercut should only occur in the angular range of the closed condition, an objective limit thus exists for an increase of the overlap or undercut surface by means of an increase of the angular range.
If the overlap or undercut surface is to be increased, it is possible to increase the diameter of the rotary closure. A closure with a greater diameter can be undesirable e.g. on a handbag.
Another way of increasing the overlap or undercut surface consists in increasing the depth of the overlap or undercut in radial direction. However, this measure likewise reaches a limit, which results from this constructive measure itself and from the special properties of the magnetic force, which will be explained below:
When pulling the closure halves together, the parts snapping into each other get in contact in that the locking piece moves a predetermined distance against the resilient and hence yielding locking element, until snapping into place occurs. This distance is the greater the further the locking element must be pushed away in radial direction, i.e. or proportionally increasing compressive force is required to overcome the likewise proportionally increasing spring force of the locking element. It is known, however, that magnetic forces have a non-linear profile and greatly increase only at close range. Since the magnetic force should, however, pull the closure together automatically and thus must overcome the spring force, it is required to select a particularly strong magnet to overcome a long spring deflection, which magnet overcomes the initial spring force already at a greater distance. However, this leads to the demand for a greater, heavier and more expensive magnet. In addition, the magnetic force at close range, i.e. in the condition snapped into place, is higher than required. This in turn requires a greater effort on opening, which is undesirable, however, e.g. for handbags, since these closures should have a soft and pleasant haptics.